Well preforating



Dec. 29, '1964 J. w. RHEA 3,163,112

WELL PERFORATING Filed Aug. 2, 1962 2 Sheets-Sheet l PRIMA CORD I3 I I; 25

GLASS OR MET COLLAPSE 1 l EXPLOSIVE VESSSEL r a CHARGE SHAPED CHARGE 29 33- 7 =7 l4 ll 39 5 -ATMOSPHER|C PRESSURE INVENTOR.

5| JOHN w. RHEA,

BYW 5 ATTORNEY.

Dec. 29, 1964 J. w. RHEA WELL PERFORATING 2 Sheets-Sheet 2 Filed Aug. 2, 1962 OmuN ATTORNEY.

United States Patent Ofiice 3,163,112 Patented Dec. 29, 1964 3,163,112 WELL PERFORATING John W. Rhea, Monahans, Tern, assignor, by mesne assignments, to Jersey Production Research Company, Tulsa, 02:121., a corporation of Delaware Filed Aug. 2, 1962, Ser. No. 214,387 1 Claim. (Cl. 102-20) This invention relates to well perforating, and more particularly to apparatus for minimizing damage to well casings and cement bonds produced when perforating with bullets, explosive jets, and the like.

When a borehole has been drilled to a given depth in the earth for the purpose of recovering earth fluids therein, it is customary to line the borehole with a tubular casing string and to cement the casing string to the surrounding earth formations. In order to open fluid communication between the interior of the casing string and a fluid productive formation, it is common practice to. perforate the casing string and the surrounding cement sheath by means of bullets or explosive jet charges. The usual practice is to simultaneously detonate a plurality of explosive jet charges to produce a multiplicity of perforations. A common type of perforating gun utilizes an elongated support means or housing. At least one, and preferably a plurality of explosive charges are affixed to the support means, and a line explosive such as Primacord connects together detonating caps for detonating the explosive charges. The line explosive in turn is detonated by an electrically activated squib or firing cap. The substantially simultaneous detonation of the line explosive and the multiplicity of explosive jet charges releases suddenly a tremendous amount of energy within the well bore that can rupture or otherwise severely damage not only the casing string but also the surrounding cement sheath. As a result, subsequent production and Workover operations are rendered more complex. It is also common practice to detonate one or a few explosive jet charges to produce one or a few perforations.

In accordance with one aspect of the present invention there is provided at least one sealed enclosure in close proximity to the explosive charge or charges for absorbing the force in the well created by detonation of the explosive charge or charges. It has been found that inclusion of such a sealed enclosure minimizes the damage done to the casing and cement sheath by detonation of explosive charges in the well.

In accordance with another aspect of the invention, production is initiated from a productive earth formation through a cased well bore by lowering the pressure in a well bore zone opposite the productive earth formation and explosively perforating the casing liner while simultaneously releasing the pressure in the well bore zone to well bore pressure. Preferably, this is accomplished by positioning a frangible, sealed enclosure in the well bore opposite the productive earth formation and simultaneously explosively perforating the casing liner and rupturing the frangible enclosure.

Objects and features of the present invention not ap parent from the above discussion will become evident upon consideration of the following detailed description thereof taken in connection with the accompanying drawings, wherein:

FIG. 1 is an elevational view of an embodiment of the invention making use of frangible low-pressure bottles;

FIG. 2 is an elevational view, partially in cross section,

of another embodiment of the invention making use of a of a piston cylinder at substantially atmospheric pressure in fluid communication with the interior of the perforating gun; and

FIGS. 4 and 5 are cement bond logs illustrating the eflicacy of the invention.

With reference to FIG. 1, there is shown an elongated explosive charge support means which comprises a flexible rod 4 afiixed to a suspension cable 1 having one or more electrical conductors therein. nected to the cable 1 by a cable head 3 including a squib or firing cap (not shown) connected to the electrical conductors in the cable so as to be activated by electrical current transmitted from the earths surface through the electrical conductors. A plurality of explosive perforating means 11, here shown as explosive jet shaped charges, are aflixed to the elongated rod 4 by means of straps 15. Each of the perforating means 11 is provided with a firing cap 14; the caps and the squib are interconnected by means of a line explosive 13 such as Primacord. Immediately above each of the shaped charges 11 is aflixed a frangible sealed enclosure, here shown as a glass or thin metallic low-pressure bottle 5, which isv affixed to the rod 4 by means of straps 9. The bottles 5 have a gas therein at a suitable low pressure, preferably between 10.0 and 14.7

p.s.1.a.

When an electric current is sent through the conductors in cable 1 to activate the squib in cable head 3, the Primacord 13 and the various explosive perforating means 11 are substantially simultaneously detonated. The energy released in the well bore upon detonation of the Primacord and explosive charges readily shatters the bottles 5, and much energy is absorbed by the implosion of the bottles. However, the jets directed laterally of the rod 4 against the surrounding casing from the explosive perforating means 11 are not affected by the implosion of bottles 5 but serve to perforate the casing in the usual manner. After perforation of the casing, production of oil and/or gas is initiated in the usual manner.

The embodiment of the invention illustrated in FIG. 2 comprises an elongated cylindrical housing 21 aflixed to a cable head 23 containing a squib (not shown). A plurality of explosive charges 25 are vertically spaced apart inside the housing 21 and positioned so as to direct explosive jets or bullets laterally of the longitiudinal axis of housing 21. Each of the explosive perforating means 25 is provided with a cap 29 interconnected by a line explosive 27 in the same manner as in the embodiment of FIG. 1. At the lower end or upper end (shown here as the lower end) of the housing 21 there is affixed an elongated piston cylinder 35 having inwardly extending annular flanges 33 and 44 at or near the upper and lower ends thereof. Pistons 37 and 41 are positioned in the cylinder 35 in sliding sealing engagement therewith. The seal-s between the piston and the cylinder are provided by piston rings 39 and 43. The lower end of the piston cylinder 35 is ported by port'45.

When the Primacord 27 and explosive perforating means 25 are detonated, the energy released into the borehole and inside the housing will be effective to force piston 37 downwardly and piston 41 upwardly. The energy suddenly released in the well bore thus will be absorbed by the gas in the chamber between pistons 37 and 41 and will be more or less slowly released back into the well a The effect of the pistons 37 and 41 is somewhat like that of a pulsation dampener on the discharge end bore.

The flexible rod 4 is con- J sealed as by a plug 51. A free piston 37 is positioned in the upper end of cylinder 55 and is in sliding sealing engagement with the piston cylinder 55. Piston rings 39 are affixed around the periphery of piston 37 to provide a seal between the piston and the cylinder. A shear pin 53 is located below the piston 37 for holding the piston in the position shown as the apparatus is lowered into a well. A gas within the piston cylinder below piston 37 is at a pressure low compared to the well bore pressure, such as atmospheric pressure.

When the explosive perforating means are detonated, a substantial portion of the energy released thereby will be exerted on piston 37 to shear the shear pin 53. The energy thus will be absorbed by the reduced pressure in the cylinder 55 to minimize casing and cement sheath damage.

FIGS. 4 and 5 illustrate actual cement bond logs utilizing a logging device such as described on page 3593 of the Composite Catalog of Oil Field Equipment and Services, 24th edition. The current bond logs of FIG. 4 were obtained before and after a well had been perforated in the conventional manner. Increasing logging signal is indicative of decreasing eflectiveness of the cement bond to the casing. It is apparent that as a result of the art of perforating, a large amount of damage was done to the cement sheath surrounding the casing. The cement bond logs of FIG. 5 were obtained from a nearby well perforated under similar circumstances utilizing a perforating gun similar to the one illustrated in FIG. 1. It is apparent from an inspection of the cement bond log that little or no damage was done to the cement sheath as a result of the act of perforating.

The invention is not to be restricted to the specific structural details or arrangement of parts herein set forth, as various modifications thereof can be effected without departing from the spirit and scope of the invention.

The objects and features of the invention having been completely described, what I wish to claim is:

In a well perforating gun comprising an elongated explosive charge support means, at least one shaped, explosive-jet perforating charge afiixed to said support means for perforating in a direction away from the longitudinal axis of said support means, and means connected to said explosive charges for detonating said at least one charge, the improvement comprising:

a piston cylinder aflixed to said support means, pistons at both ends of said cylinder and in sliding, sealing engagement with the cylinder wall, and annular flanges having a central opening therein at each end of said cylinder for limiting outward movement of said pistons, port means for exposing said pistons to well fluid, said cylinder being filled with gas at substantially the hydrostatic pressure of fluids in the well at the level thereof to be perforated.

References Cited in the file of this patent UNITED STATES PATENTS 2,695,065 Baker et al Nov. 23, 1954 2,742,857 Turechek Apr. 24, 1956 2,749,840 Babcock June 12, 1956 2,797,892 Ryan July 2, 1957 2,909,120 Lebourg Oct. 20, 1959 2,965,031 Johns Dec. 20, 1960 3,043,379 Porter et a1. .Tuly 10, 1962 3,075,463 Eilers et a1. Jan. 29, 1963 

